Sometimes choosing the wrong support material can have devastating consequences…
The Terran Space Academy is dedicated to educating you so you can avoid these mistakes and have a long and healthy career in the space industry…
This course is the first in a series on Space Engineering…
This lesson will be covering Composite Materials for Aerospace Applications…
(and where I sometimes say millimeter... I meant micrometer... I have no mu key...)
Composites are light and can be shaped into nice curves for aerodynamics, they are strong at normal temperatures, but most cannot survive temperatures above 200C, and become very brittle and weak with cryogenic temperature exposure. The most successful use of composite materials to date is the Electron Rocket by Rocket Lab, a US-New Zealand company. This is the most innovative space company flying next to SpaceX. Like SpaceX they have embraced vertical integration, designing their own cryogenic systems that allow them to have composite liquid oxygen tanks. This is a very big deal as it is extremely hard to get a fabric to contain a gas or liquid, and cryogenic temperatures usually cause composite materials to become too brittle and fail. This company has not only solved this problem but designs its own cryogenic valves. Rocket Lab also designs the avionics and control computers keeping it in control of its designs and making it less dependent on outside vendors, which may not be as dedicated to quality control as your company.
These composite rockets have proven themselves as an excellent choice for small payload deployment and composite materials are the perfect choice for the spaceplanes and suborbital capsules we covered. But as Elon Musk discovered when he tried to use composite materials for his innovative Starship design…once you get to larger volumes and colder cryogenic temperatures…and you must reenter the atmosphere from orbital or translunar velocities…these materials are a poor choice. Remember that volume increases cubed while surface area is squared. Let us look at where trying to use composite materials in the wrong application led to the shutdown of an excellent spaceship design and the wasting of hundreds of millions of dollars.
The X33 was going to be a single stage to orbit spaceship to replace the space shuttle. It was going to use an innovative linear aerospike engine that could have revolutionized rocket propulsion. Everything was going great and the ship was almost completely built when they hit a snag. Composite materials had been chosen for the fuel tanks. The funding for the ship had been predicated on this application. The engineers tried and tried to solve the problem of a large composite tank being strong enough to hold the volume necessary to get this massive ship into orbit. The engineers had to make the composite layers thick to prevent gas leakage and prevent fracturing from the very cold cryogenic fuels. Especially the liquid hydrogen. Liquid hydrogen must be kept below 20 kelvin and this extreme cold will make almost anything brittle enough to fracture. While the materials could have worked with liquid oxygen and supercooled methane or RP-1, they could not get it to work for hydrogen. The engineers went to the administrators and told them that they could easily solve the problem with aluminum alloy tanks, but it could not be done with composite tanks. The administrators told the engineers that they had to use composite tanks, or the project would be canceled…and it was. This is a very good lesson in why allowing non-scientists and non-engineers to make critical design choices for a spaceship is a very bad idea…the N1 failed because of administrative interference in design choices…and the X33 was canceled because the administrators…trying to make politicians happy instead of building the best possible ship...failed to make the necessary changes to save the X33.
aerospaceengin...
www.wired.com/...
www.rocketlabu...
www.virgingala...
Corrections: a few places I keep saying millimeter instead of micrometer... no mu key on my keyboard but I think the error is obvious. 10mm would be the size of a little finger.